Studies are proposed on the phospholipase A2 from (1) cobra venom Naja naja naja) which is mong the smallest and most well-studied enzymes of complex lipid metabolism and from (2) human amnionic membranes which have been implicated in the generation of arachidonic acid for prostaglandin biosynthesis. Lipolytic enzymes are unusual in that they act physiologically on substrates that are part of complex aggregated structures such as lipoprotein complexes, intracellular fat droplets, bile acid-lipid mixed micelles, or membranes, rather than on phospholipids or triglycerides which are molecularly dispersed. Both in vivo and in vitro, these enzymes require a lipid-water interface to act and these studies focus on its role in the mechanism of action of these enzymes. Specific studies on the cobra venom phospholipase A2 are aimed at simplifying its purification, defining the role of its recently discovered "activator site" in its mechanism, determining whether the active enzyme is a monomer or dimer, describing the amino acids important for catalysis and activation, determining the nature of phospholipid binding to the enzyme, describing the individual steps in the mechanism, and determining how the physical state of the substrate affects enzymatic catalysis. Specific studies on the phospholipase from human amnionic membranes are aimed at purifying and characterizing the enzyme, determining its substrate specificity which has been suggested to play a specific role in arachidonic acid release, and investigating the effects on this enzyme of drugs and hormones implicated in prostaglandin control in order to better understand the role phospholipase A2 plays in the in vivo control of prostaglandin biosynthesis.